Generally, plasma etching refers to a form of plasma processing used to fabricate integrated circuits. It typically involves a high-speed stream of glow discharge (plasma) of an appropriate gas mixture being shot at a wafer placed on a stage. Typically, plasma is produced from the gas mixture using a high frequency electric field. The plasma can contain ions and/or neutral atoms and radicals. Typically, a bias RF electrode is placed on the stage beneath the wafer to couple to a radio frequency (“RF”) bias power source and to create an electric field near the wafer to achieve more anisotropic etch profile. Generally, the electric field is created by the bias RF electrode that acts as a cathode, and a chamber wall that acts as an anode.
FIG. 1A shows a top view 100 and FIG. 1B shows a side view 110 of a typical Bias RF electrode 101. The typical Bias RF electrode 101 is a single piece of metal, as shown in FIGS. 1A and 1B. Generally, an electrical field near the wafer in the etching chamber created by the typical Bias RF electrode is not uniform over the wafer. The strength of the bombardment of the ions and/or neutral atoms and radicals for etching is not uniform over the wafer because of the non-uniform electric field created by the typical Bias RF electrode. Variations of the bombardment strength results in the non-uniform etching of the wafer.
Generally, a chip is fabricated using a photomask that provides a pattern for an integrated circuit layer on the chip. The accuracy of this pattern is critical in manufacturing the chip. Critical dimension (“CD”) uniformity is an important property of the patterned photomask. The pattern on the photomask is typically created using a plasma etching technique. Etching the photomask in the plasma chamber using the typical Bias RF electrode as a cathode can introduce etch non-uniformity that can severely impact the CD uniformity of the photomask.